Self-retaining sutures have previously been developed for use in wound closure, and other surgical procedures such as plastic surgery, see for example US Patent Application No. 2005/0267532 to Wu. These sutures contain tissue retainers (e.g. barbs) placed in a variety of different configurations along the suture fiber that when implanted project from the suture surface into tissue and resist movement in a direction opposite to the direction the tissue retainer faces.
The process of cutting tissue retainers into suture fiber decreases the cross-section of fiber that can support a load, and therefore cutting tissue retainers into a suture fiber decreases the straight pull tensile strength of the suture fiber. The straight pull tensile strength of a self-retaining suture is very important for several reasons. First, during implantation of the suture, force is applied along the axis of the suture fiber. The straight pull tensile strength of the self-retaining suture must be sufficient to prevent breakage of the suture during implantation. Second, immediately after placement, the suture must be strong enough to resist forces applied by the body, and particularly by strong muscles. For example, if the self-retaining suture is used in the face, the suture must be strong enough to resist forces applied by the patient when smiling, laughing, eating, frowning, etc. Third, if the self-retaining suture is absorbable it is vital that cutting tissue retainers in the suture does not decrease the strength retention profile so that it is too short to allow replacement of the suture's load carrying capacity by the body. For example, there should be enough time for the body to generate sufficient fibrotic tissue and adequate support before there is a critical loss of the suture's tensile strength (including the strength exerted by the tissue retainers).
Unfortunately, commercially available self-retaining absorbable sutures do not meet the US Pharmacopeia standard for average minimum knot-pull strength (measured by straight pull). For example, to meet the USP tensile strength for an absorbable suture of size 3-0, a surgeon must not only use a size 2-0 of Quill's Monoderm (a copolymer of glycolide and ε-caprolactone) self-retaining suture (see Angiotech product package insert P/N 03-5296R2), but the size 2-0 Quill Monoderm self-retaining suture also must have an oversized diameter. The size overage may be an increase in suture diameter of up to 0.1 mm. So, it is necessary not only to use a suture that is one size larger on the USP standards scale, but that is also oversized by up to 0.1 mm in diameter. Another example is Quill's PDO (polydioxanone) self-retaining sutures. To meet, for example, the USP tensile strength of a size 3-0 suture, a surgeon must not only use a size 2-0 of Quill's PDO (polydioxanone) self-retaining suture (see Angiotech product package insert P/N 03-5278R3), but also the size 2-0 suture must also be oversized in diameter by up to 0.1 mm. Greenberg, J. A. The use of barbed sutures in obstetrics and gynecology, Rev. Obstet. Gynecol. 3(3):82-91 (2010) also states clearly “Owing to its decreased effective diameter as a result of the process of creating barbs, barbed suture is typically rated equivalent to 1 USP suture size greater than its conventional equivalent. For example, a 2-0 barbed suture equals a 3-0 smooth suture”. Consequently, surgeons are currently required to use suture diameters much larger than desired in order for the strength to be adequate for the repair, create suture tunnels in tissue that are larger than necessary, and in certain cases use sutures that are less pliable than might be desired.
Thus, in the practice of surgery there currently exists a need for absorbable self-retaining sutures with tensile strengths that meet or approximate (i.e. do not stray too far from) the standards of the US Pharmacopeia. These sutures would allow the surgeon to use smaller diameter sutures than is currently possible without compromising the tensile strength of the suture. The use of these absorbable self-retaining sutures would also decrease the amount of foreign material that needs to be implanted in the body, decrease the size of suture tunnels in a patient's tissues, and also provide more pliable suture options.
It is therefore an object of this invention to provide absorbable monofilament fibers and self-retaining sutures with high tensile strengths.
It is a further object of this invention to provide absorbable self-retaining sutures with smaller diameters and high tensile strengths.
It is yet a further object of this invention to provide absorbable self-retaining sutures with straight pull tensile strengths that equal or exceed the average minimum knot-pull tensile standards set by the United States Pharmacopeia (USP) wherein the self-retaining sutures are not oversized more than 0.1 mm in diameter.
It is still a further object of this invention to provide absorbable self-retaining sutures with high tensile strengths that are also pliable.
It is yet another object of this invention to provide methods to produce absorbable self-retaining sutures that have high tensile strengths.
It is still yet another object of this invention to provide methods to produce fibers of P4HB and copolymers thereof that have pronounced sheath-core structures wherein the sheath is harder than the core.
It is even yet another object of this invention to provide methods to implant absorbable self-retaining sutures that have high tensile strengths.